In the wake of our investigation into whether retail Radeon R9 290X cards are slower than press samples, AMD has issued a statement on these matters. Here's the text in full:

Based on feedback from the enthusiast community, we’ve implemented an all new PowerTune mechanism in the AMD Radeon R9 290 series that exploits the full capability of the individual GPUs rather than clamping performance to a least-common-denominator type of capability ...